Have you ever wondered when and why is your boiler running and heating your home? Do you want to automate your heating system with Arduino? The OpenTherm shield is designed for you. It will allow you to monitor and control your OpenTherm boiler with Arduino.

OpenTherm is simple protocol implemented on 2-wires bus allowing boiler and thermostat to communicate. They exchange various information including status, temperatures and set points. The protocol is easy to read and with this shield you can easily get or alter all the available information.

Features

OpenTherm slave interface to communicate with a boiler

OpenTherm master interface to communicate with a thermostat

can implement master, slave and gateway modes

RX and TX LED indicators

5V 3A built-in power supply

Arduino UNO compatible shield

Available data and commands

room temperature

room temperature set point

heating water temperature

return water temperature

domestic hot water temperature*

domestic hot water pressure*

domestic hot water flow rate*

outside temperature*

boiler status (running / not running / error)

modulation level

exhaust temperature*

statistics how long the boiler was running

* note that these are available only if your boiler is equipped with necessary accessories

What you can create with it?

Thermostat - use the shield to build your own Arduino-based thermostat to fully take over your boiler and home heating. Perfect for home automation. This application only requires an external 5V power supply.

Gateway/Monitor - place an OpenTherm shield into the lines between the existing boiler and thermostat and create a monitor to watch when how the boiler is heating your home.

Man-in-the-middle - instead of just listening to the communication like in gateway mode you can also alter the communication that is happening between the boiler and thermostat and adjusts the behavior as you want. Perfect for creating your own heating regulator.

Supported boilers

Every boiler that supports OpenTherm+ is supported. See your boiler manual for OpenTherm capabilities. There is a slight chance that your boiler won't be compatible due to manufacturer's customization of OpenTherm protocol.

Arduino support and library

I wrote an Arduino library to create a simple API over the OpenTherm protocol. It contains examples for all the listed modes and it will allow you to easily start programming your own application. More information on a github.com project page. The library is available in the Arduino libraries store.

OpenTherm shield requires an external 24V 500mA DC power supply which is not included in the kit.

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